In connection between optical fibers, in order to prevent reflected return light on an optical fiber end face, it is generally known that the optical fibers having end faces formed into an oblique shape are made to face each other, and it is proposed to position a pair of optical fibers in grooves, the axes of which are displaced from each other, such that the end faces of the optical fibers which face each other are substantially parallel to each other and the emission optical axis of one of the optical fibers coincides with the core center of the other optical fiber (see PTL 1).
On the other hand, as an optical fiber with lens, there is known an optical fiber collimator which emits light emitted from an optical fiber as parallel light using a lens, and there is known an optical fiber with GRIN lens which uses a GRIN lens (gradient index lens) as the lens and has the end part of the optical fiber welded to the center of the GRIN lens.
In connection between the optical fibers with lenses, by coaxially disposing the optical fibers with lenses such that the optical fibers with lenses face each other, light emitted from one of the optical fibers becomes parallel light by one of the lenses, and the parallel light is focused by the other lens and enters the other optical fiber. In the connection between the optical fibers with lenses serving as optical collimators, a sufficient interval is provided between lens end faces (see PTL 2 shown below).
In the connection between the optical fibers with lenses described above, there is known a connector in which the end part of the optical fiber with lens is mounted to the center of a ferrule and a pair of the ferrules are coaxially made to abut on each other by a cylindrical sleeve (see PTL 3 shown below).
In the connection between the optical fibers with lenses (optical fiber collimators) as well, the prevention of the reflected return light is a major task and, in order to achieve this task, it is known that the emission end face of the lens is obliquely formed, and it is known that, in order to connect the optical fibers with lenses having the obliquely inclined emission end faces, the optical fiber with lens is supported by a groove on a board (see PTL 4 shown below).